Document recognition systems

ABSTRACT

A bank note recognition system includes an optical analyser for scrutinising the watermark, selected areas of print on the surface of the bank note, the wire band in the bank note and the density of the paper of the bank note. The analyser in its simplest form includes a lamp for illuminating a discrete area of the bank note and two photo electric elements on opposite side of the bank note for respectively sensing the transparency and reflectivity of the discrete area of the bank note. The analysis will provide indication whether the bank note is genuine and will accept the bank note only if considered to be genuine.

United States Patent Martelli et al. Jan. 1, 1974 [54] DOCUMENTRECOGNITION SYSTEMS 3,239,814 3/1966 Willie 250/219 DO [76] In e tors ro artel, V a Sel a 1, 3,443,107 5/1969 Modglin 209/DIG. 2

Compiobbi; Mario Martelli, Viale Talenti 63y Firenze both of ItalyPrimary Exammer-Allen N. Knowles Attorney-Nichol M. Sandoe et al. [22]Filed: Oct. 12, 1972 [21] Appl. No.: 296,853 [57] ABSTRACT A bank noterecognition system includes an optical [30] Foreign Application PriorityData analyser for scrutinising the watermark, selected areas Oct. 15,1971 Italy ..9724A/71 Of Primt the Surface Ofthe bank note, the Wireband in the bank note and the density of the paper of the 52 1 75 209/17 250/219 DQ, bank note. The analyser in its simplest form includes azoo/DI 2 lamp for illuminating a discrete area of the bank note 51 Int.Cl. B07 5/342 and two photo electric elements on Opposite Side of [58]Field of Search 209/75, 111.7, DIG. 2; the bank note for respectivelySensing the transpar- 250/219 DQ ency and reflectivity of the discretearea of the bank note. The analysis will provide indication whether the[56 References Ci bank note is genuine and will accept the bank noteUNITED STATES PATENTS only if considered to be genuine. H

2,941,187 6/1960 Simjian 209/010. 2 13 Claims, 11 Drawing FiguresDOCUMENT RECOGNITION SYSTEMS BACKGROUND OF THE INVENTION 1. Field of theInvention The invention relates to document recognition systems forrecognising documents such as bank notes.

2. Description of the Prior Art Previously proposed bank noteExamination systems have involved a search of the bank note surface byphoto electric means for recognisable patterns and contours inconjunction with detecting other characteristics of the bank note. Suchas the detection of luminous or magnetic inks such systems have notproved to be sufficiently reliable or sufficiently flexible.

It is an object of the invention to provide an improved system forrecognising documents.

SUMMARY OF THE INVENTION The invention provides a document recognitionde vice, an optical analyser comprising support means for supporting adocument to be analysed, light source means mounted to direct light at apredetermined area of the document, a first photo sensitive membermounted to receive from the light source means, light which has passedthrough the predetermined area of the document and providing an outputindicative of the light received, a second photo sensitive membermounted to receive light from the light source that has been reflectedfrom the predetermined area and providing an input indicative of thelight received, reference means for establishing reference ranges forthe transparency and reflectivity of valid documents, and comparisonmeans connected to receive the output signals from the first and secondphoto sensitive members and connected to the reference means to comparethe output signals with the reference ranges to determine the validityof the document in dependence upon the result of the comparison.

In the specification and claims, the phrase banknote includes (exceptwhere the context indicates otherwise) a counterfeit as well as agenuine banknote.

BRIEF DESCRIPTION OF THE DRAWINGS Banknote recognition systems embodyingthe invention will now be described by way of example, with reference tothe accompanying diagrammatic drawings in which:

FIG. 1 is a cross section through an optical analyser of the systems;

FIG. 2 is a cross section through one of the systems, for analysing abank note in motion;

FIG. 3 is another of the systems, for analysing a bank note in motion;

FIG. 4 is a circuit diagram of a reversing mechanism for the system ofFIG. 3;

FIG. 5 is a circuit diagram of a gated control circuit for the systemsof FIG. 2 and 3;

FIG. 6 is a part cross-sectional view of an adjustable optical analyserfor use in the systems;

FIG. 7 is an under plan view of the analyser of FIG.

FIG. 8 is a part cross-sectional view of another analyser for use in thesystems and having a plurality of sensing head apertures;

FIG. 9 is an underneath view of the analyser of FIG.

FIG. 10 is a block diagram of the control circuit for a comprehensiveoptical analyser for use in the systems; and

FIG. 11 is a block diagram of part of the control circuit of FIG. 10 inmore detail.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an opticalanalyser for determining the transparency and reflectivity of adocument, for example a bank note. The analyser includes a light source1 providing light of i a desired wavelength. The light source can be amicrolamp having a built-in or an external lens, and be provided with aselection of chromatic filters. The analyser also includes twophotosensitive elements 3 and 5 (for example photo resistors or photodiodes). The element 3 is located on the opposite side of the bank note7 to the light source 1 and provides an indication of the transparencyof the note. The element 5 lies on the same side of the bank note as thelight source 1. The bank note 7 is arranged to be driven through theanalyser along guide 8.

In order to make the two measurements of transparency and reflectivitysimultaneously at a selected point on the bank note the element 3 islocated on the same axis as the optical axis of the light source, whichoptical axis is inclined with respect to the plane of the bank note 7under test, and the element 5 is located in a position in which it issubstantially symmetrically positioned with respect to the element 3 buton the oppo site side of the bank note. The source 1 is rotatable aboutits own axis by means of a lamp holder 9 so as to orientate the image ofthe filament on the bank note in any desired manner, as will bedescribed in more detail hereinafter. The data derived from thesimultaneous transparency and reflection measurements enables the noteto be speedily recognised.

A scrutiny of the paper on which the bank note is printed is performedby making a plurality of transparency measurements at discrete points onthe bank note. Discrete points are located by using an edge of the banknote or a detail of the print on the bank note as a reference location.The value of the transparency measurement must lie within upper andlower limits if the bank note is to be considered genuine. The upper andlower limits are determined by the type of paper employed in themanufacture of legal bank notes.

The presence of a watermark in a particular zone of the bank note can bedetected as a variation in the transparency of the bank note. In thecase of an authentic watermark, variations in transparency but not inthe reflection may be noted as the bank note is scanned. Appreciablereflection variations can be observed where the watermark is counterfeitand made by means of oil stains or paraffin, for example. Therefore,comparison of the transparency and reflectivity of the watermark ofthebank note enables it to be recognised. The above criteria can bebuilt into electronic circuits which can then be used to distinguishcounterfeit from real bank notes.

Some bank notes have a built-in metallic strip. An optical analysis ofthis strip can also be used in determining whether or not the bank noteis genuine.

In the case of a forged bank note the wire may have been applied to theouter surface of the bank note or have been simulated as a mark on theouter surface. In

either case the result will be a change in the reflectivity of thesurface.

In order to distinguish a genuine wire from such forgeries, atransparency measurement must be taken at the location of the wire andin addition reflection measurements must be made from opposite sides ofthe bank note at the same point in the bank note. The reflectionmeasurements may be taken at separate instants but should preferably bemade simultaneously.

It will be appreciated that if a genuine bank note becomes marked duringuse and the mark is somewhat similar to that of a wire then theresultant measurements can cause the bank note to be rejected eventhough the bank note is genuine. It is, however, preferable to reject agenuine bank note rather than to accept a counterfeit one.

When scrutinising the bank note wire, the sensitivity of the analyser ispreferably increased. Sensitivity can be increased by placing a mask infront of the lamp or the photo electric element. The mask has a slotextending in the direction of the wire so that only a narrow area of thebank note is scrutinised.

Instead, sensitivity can be improved by orientating the sleeve 9 whichholds the illumination source so that the filament of the lamp is inalignment with the bank note wire.

In order to make the counterfeiting of a bank note more expensive andmore complex, some portions of the drawing of the bank note are made bya relief printing method. Relief print provides a much lower reflectionthan print made by conventional methods and inks. By using a diaphragmin conjunction with the lamp, (the diameter of the hole, of thediaphragm advantageously being of the order of 0.3 mm) a reflectionanalysis can be made of a sufficiently small point that very smalldetail of the banknote surface can be observed. In order to locate aselected point on the banknote, the scanning of the banknote is onlyinitiated when a reference point on the banknote, for example an edge ofthe banknote or a major detail of the subject printed on the banknotereaches a predetermined position. Once the detail is located thescanning will determine whether or not the reflection from the detaillies within the prescribed limits for a genuine banknote.

The above method of examining a selected detail of the bank note can beextended to examining another selected detail so that the mutualposition of the two details can be checked against that of a genuinebank note.

By activating and de-activating the transparency and- /or reflectionphoto sensitive elements of a single analyser in accordance with apredetermined programme as the bank note passes through the analyser ata constant velocity, measurements cna be made of discrete areas of thebanknote. The resultant measurements are then compared with upper andlower limits and if all the measurements be found to be within theseupper and lower limits, the banknote will be accepted as genuine.

Instead of using a single analyser to examine each selected point of thebank note in turn a plurality of analysers can be used to makesimultaneous measurements of all the selected points. The measurementsmay be obtained when the banknote is in motion or with a system in whichthe bank note is held in a fixed position; the analyser beingappropriately positioned with respect to the bank note. It is alsopossible to use a system in which the banknote is temporarily halted ina predetermined position, for a predetermined time (however short)sufficient to effect the simultaneous measurements.

It will be appreciated that with the system described in whichtransparency and reflection measurements are made at the same point andat the same time, it is very difficult for a counterfeit note to escapedetection, as in practice, a forger must simultaneously re-create thesame transparency and reflection conditions at the same point as thosein a conventional bank note.

The head of FIG. 1 performs both. transparency and reflectionmeasurements using only one light source. If a separate lamp were usedfor each measurement then the turning off of the transparencymeasurement lamp would lead to the acceptance of banknotes without awire and without surface marks in a selected zone. Thus for example aphoto copy of the bank note would be accepted.

The analysers described can be made more sensitive by using a colourfilter with the light source appropriate to the colour of the bank noteto be examined and by making the photo electric elements speciallysensitive to that selected colour.

' FIG. 2 illustrates a bank note recognition system for analysing a banknote in motion. The system includes an ingress switch 11 (formed by amicro switch or a photo electric relay, for example) which is arrangedto be triggered by the leading edge of the bank note to energise theelectric circuits of the system. When the switch 11 is triggered,rollers 17A are energised to feed the bank note along a guide track 13through an optical analyser 15. The optical analyser 15 can take theform shown in FIG. 1.

The analyser l5 scrutinises selected discrete points of the bank noteand determines whether or not it considers the bank note to be genuine.As the bank note emerges from the analyser it is fed by rollers 17Bfurther along the path 13 until its leading edge triggers a reset switch19 (a micro switch or a photo electric relay for example) whereupon theanalyser l5 and the rollers 17A are de-energised in readiness to receivethe next bank note. This enables the system to start processing the nextbank note before the processing of the previous bank note has beencompleted.

The guide track 13 includes a plurality of stretching rollers (notshown) to maintain the bank note flat.

After the bank note has triggered the switch 19 it is fed towards anelectromechanical switch 21 which is controlled by the analyser 15 todirect the bank note along one or other of two paths 23 and 25 independence on whether or not the bank note is considered genuine. If thenote is not considered to be genuine it passes along the path 25 whileif it is considered to be genuine it is diverted along the path 23. Anoutlet switch 27 (a micro switch or photo electric relay, for example)is triggered by the bank note to return the switch 21 into its initialposition each time a bank note is accepted as genuine.

It is advantageous that the distance between the switches 11 and 9 issmaller than the length of the bank note. The distance between theswitches 19 and 27 should also be smaller than the length of the banknote.

FIG. 3 shows another bank note recognition system in which parts similarto those in FIG. 2 are similarly referenced. In operation the bank noteis fed into an inlet 29 and along guide 31 having a portion 31a passingthrough the optical analyser 15. The portion 31a of the guide 31 isinclined at an angle a with respect to the initial portion of the guide31. An electro magnetic switch 33 is operable to direct the bank notealong the path 35 or along the path 37 in dependence on whether the banknote has been rejected or accepted. A rejected bank note is directedalong the path 35 and eventually emerges from the outlet 39. The bend inthe guide path 31l as it passes into the analyser is advantageous inreducing the possibility of damage to the analyser, for example by aperson attempting to tamper with the system by introducing a smallscrewdriver or the like into the inlet 29.

In order to reduce errors whilst scrutinising the bank notes that resultfrom the presence of folds, wrinkles or the like in the bank note (whichwould particularly affeet the reflection measurements) the bank note isstretched while it is being scrutinised. To achieve this, the two pairsof rollers 17A and 173 on opposite sides of the analyser are arranged sothat the second pair of rollers 17B drives the bank note at a greaterspeed than the first pair.

In order to avoid the acceptance obtained by a genuine bank note frombeing used to provide acceptance for a subsequent forged bank note thatclosely follows the genuine bank note, a system is provided whichautomatically separates subsequently introduced bank notes from thefirst bank note. The system comprises a pair of initial rollers 41 whichare driven independently of the rollers 17A and 178. The rollers 41 aretriggered by a normally open contact of the switch 11 and a normallyclosed contact of switch 19. Because the distance between the switches11 and 19 along the guide path 31 is arranged to be shorter than thelength of the bank note, the trailing edge of the bank note will stilllie between the rollers 41 when switch 19 is triggered by the leadingedge of the bank note. The actuation of the switch 19 will lock therollers 41, but the bank note will continue to be driven along the pathby the combined action of the pairs of rollers, 17A and 17B and anysubsequently introduced bank note will not be advanced.

An excessive thickness of the bank note caused for example by thesuperimposition of foreign elements (gummed paper, adhesive paper or thelike) on the bank note or in the case of a forgery where the naturalthickness of the bank note is greater than that of a genuine bank note,can be detected by means of a mechanical feeler (a micro switch forexample). When this thickness is sensed, the direction of drive of therollers 41 is reversed to return the bank note back to the inlet 21. Bythis means the bank note is prevented from entering the analyser andother parts of the system where it could cause the system to lock orseize up. The period for which the rollers 41 are driven in reverse mustlast for a sufficient time to ensure the return of the bank note. Thiscan be achieved by using electric and electronic timing circuits, forexample as shown in FIG. 4.

In FIG. d the timing circuit includes a motor 45 for driving the rollers41, a feeler 47 which may form part of the switch 11, and a delaycircuit 51 having a switch operated by the feeler 47. The delay circuit51 controls an electromagnetic switch 53 for reversing the power supplyto the motor $5.

The analyser 15 as it scrutinises the various selected discrete areas ofthe bank note passes the information derived to gate and bistablecircuits or to electromagnetic relays to be memorised.

FIG. 5 shows a circuit having two relays 55 and 57 (only the contactsbeing shown). The relay 57 stores information given concerning thewatermark while the relay 55 stores information concerning the bank notewire. The contacts of the two relays are connected in series with theelectromagnetic switch circuit 21 or 33 (see FIGS. 2 and 3). Only whenthe wire and the watermark have been accepted as genuine will theelectromagnetic switch 21, 33 be operated to be followed by thecollection of the bank note in an appropriate container and the start ofa merchandise dispensing func tion for which the bank note was inserted.

It will be seen that every step in the analysis of the bank note must beaccompanied by a positive response before the bank note is accepted asgenuine. Thus any malfunction of the analyser in failing to provide apositive response even though a bank note is genuine will result in thereturn of the bank note rather than its retention and acceptance.

The analyser need not be limited to scrutinising the same predeterminedarea of the bank note but can be readily adjusted to scrutinise adifferent area. FIGS. 6 and 7 show an adjustable analyser in which asupport head 61 houses a first assembly 63 carrying a source and a photoelectric sensor and a second assembly 63A carrying a second photoelectric sensor, the light source and photo-electric sensors beingpositioned as in the arrangement of FIG. 1. The head 61 has a pair ofstop pins 65, 67 which can engage a selected one of a plurality ofdiscrete pairs of holes 69 in a base member 71, thereby enabling thehead to be accurately located in a plurality of discrete positions onthe base 71. By this means the head can be arranged to scrutinisedifferent areas of the bank note as desired. I

A similar result can be obtained with the modification shown in FIGS. 8and 9 in which parts similar to those in FIGS. 6 and 7 are similarlyreferenced. In FIGS. 8 and 9 the head 61 is rigidly secured to the baseand has a plurality of pairs of apertures Ma for receiving theassemblies 63 and 63A. By locating the assemblies 63 and 63A indifferent pairs of apertures, different zones '75, 77 and '79 of thebank note can be scrutinised as it travels along the guide 81.Associated with each of the zones 75, '77 and 79 are upper and lowerlimit criteria for the output of the analyser. Thus if the output of theanalyser falls between the two limits the bank note under considerationwill be accepted as genuine.

it will be appreciated that if the system has two analysers (eachanalyser determining the transparency and the reflection of the banknote at a different point) and each analyser is capable of occupying upto ten different positions in the head, the program for any particularanalysis can be selected from one hundred different programs. This willmake it difficult for a potential forger to be sure that his bank notewill be accepted by the analyser unless be copies the whole bank noteand not just one or two particular zones thereof.

FIG. it) and 11 show a block diagram of a control system for a bank notedetection system in which the following features of the bank note areexamined:

a. the watermark;

b. the reflection from a printed surface of the bank note at twodifferent areas;

0. the wire;

d. the type of paper used;

c. the bank note thickness; and

f. the length of the bank note.

The examination of features (a) and (b) of the bank note is carried outby using an analyser such as that shown in FIG. 1. Such an analyser hasa transparency photosensitive element 103 T1 and a reflectionphotosensitive element 105 R1 corresponding to those denoted by 3 and 5in FIG. 1. The output of each photosensitive element 103 T1 and 105 R1is fed to a respective ipper limit threshold circuit 109 and 111 andalso to a respective lower limit threshold circuit 110 and 112. Theoutput of the four threshold circuits are fed to an AND gate 114.

The examination of features (c) and (d) of the bank note is carried outby using two analysers each similar to that shown in FIG. 1. Oneanalyser has a transparency photosensitive element 203 T2 and areflection photosensitive element 205 R2 while the other analyser has atransparency photosensitive element 303 T3 and a reflectionphotosensitive element 305 R3. The output of elements 203 T2 and 303 T3are fed to respective circuits 209 and 309. The outputs of thephotosensitive elements 205 R2 and 305 R3 are fed to a respective upperlimit threshold circuit 211 and 311, and also to a respective lowerlimit threshold circuit 212 and 312. The circuits 311 and 312 areconnected to an AND gate 314. The outputs from the four circuits 209,309, 214 and 314 all feed another AND gate 216 to provide an outputindicative of the presence of a genuine wire incorporated in the banknote.

The same photosensitive elements 105 R1 and 203 T2, although shownseparately, are also used to examine the print of the bank note at twopoints A and B. During examination of the print at point A, the outputof element 105 R1 is fed to upper and lower limit threshold circuits 116and 118 and the outputs of threshold circuits 116 and 118 are fed to anAND gate 120. During the examination of the print at point B of the banknote, the output of the element 105 R1 is fed to upper and lower limitthreshold circuits 122 and 124. The outputs of the threshold circuits122 and 124 are fed to an AND gate 126.

The photosensitive element 203 T3 (although shown separately) is alsoused to examine the kind of paper on which the bank note is printed. Theoutput of the element 203 T3 is fed to both upper and lower limitthreshold circuits 218 and 220. The outputs of the threshold circuits218 and 220 are fed to an AND gate 222.

The AND gates 114, 216 and 120 are connected to a switching circuit 401which is shown in more detail in FIG. 11. All the AND gates 114, 216,120, 126 and 222 are connected to a final AND circuit 501 which whentriggered feeds an output signal to a switching circuit 503. Theswitching circuit 503 has a switch which is operable to connect thepower supply 505 to an acceptance unit 51-1. The power supply 505 alsofeeds an ingress unit 507, a reset unit 509, and a thickness feeler 515for controlling the direction of the rotation of the rollers 17A and 41in the system of FIG. 3.

The output of the ingress unit 507 and also one output of the reset unit509 are connected to a line 517 that powers the analyser so that currentfrom the power source 505 to the analyser can be fed either via theingress unit 507 or the reset line 509.

The acceptance unit 511 has three outputs, one output is connected to aline 519 that controls the clearing and sorting of accepted and rejectedbank notes, another output is connected to a line 512 controlling thedispensing of merchandise for which the bank note was inserted, and thethird output is connected to a reset member of the means for clearingand sorting bank notes.

The switching unit 401 shown in FIG. 10 will now be described in moredetail with reference to FIG. 11. The three signals which arrive at theswitching unit from the circuits 114, 120 and 216 control theenergisation of respective coils 1148, 1203 and 2l6b. Each coil controlsthe operation of a switch. At the completion of the watermark analysis,the switch 114C of coil 114B disconnects the element R1 from line 403(that connects the element to the threshold circuits 111 and 1 12) andinstead connects the element to line 405. The switch C of the coil 1208when energised disconnects the line 405 from the line 407 and insteadconnects it with the line 409 to thereby couple the element 105 R1 tothe threshold circuits 112 and 124 in readiness for scrutinising point Bof the bank note. The contacts 21601 of the switch when operated by thecoil 216B, decouple the element 203 T2 from the line 411 that connectsthe element 203 T2 to the unit 209, and instead couples the element 203T2 to the line 413 which connects the element 203 T2 to the thresholdcircuits 218 and 220. At the same time the contacts 216C2 of the sameswitch close to connect the line 407 with the line 415 and therebycomplete the circuit from the element 105 R1 to the threshold elements116 and 118 thus enabling analysis of point A on the bank note to bemade.

The elements 203 T2, 305 R2, 303 T3 and 305 R3 are all arranged to liein a common plane which extends parallel to the edge of a bank note, theelements 203 D2 and 305 R3 being arranged to lie on one side of the banknote and the elements 303 D3 and 205 R2 being arranged to lie on theother side of the bank note.

In operation as soon as the bank note is introduced into the bank noterecognition system, it energises the ingress unit 507 which suppliescurrent from the source 505 to the line 517 and, through a normallyclosed contact set of the reset unit 509, to the thickness feeler 515 todrive the rollers 17A or 41. If the bank note thickness is greater thana predetermined thickness the sense of rotation of the rollers 17A or 41(see FIG. 4) is reversed, and the bank note is returned. If the detectedthickness lies within the prescribed limits for a particular bank note,the bank note continues its motion in the same direction and passes intothe optical analyser. As the leading edge of the bank note approachesthe analyser, it triggers the reset unit 509 to de-energise the rollers41. The normally open contact of the reset unit 509 is now closed and socontinues to supply current to the analysers. The normally closedcontacts of the unit 509 is open to discontinue the supply of currentdriving the first pair of rollers to prevent insertion of a fresh banknote. From this instant, forward motion of the bank note is continued bypairs of subsequent rollers while the ingress of further bank notes isprevented until the trailing edge of the present bank note emerges fromthe unit 509. As the distance along the bank note path between the units507 and 509 is smaller than the length of the bank note the leading edgeof the bank note reaches the unit 509 before its trailing edge has leftthe unit 507. This insures an uninterrupted supply of current to theline 517.

If all the inputs to the AND gate 501 are present, indicating that thebank note analysed is considered to be genuine, the switch circuit 503connects the acceptance unit 5111 to the power supply 505. Energisationof the acceptance unit 511 triggers the merchandise dispensing means(not shown), the means controlling acceptance or rejection of banknotes, and a resetting device of the latter means.

As the bank note continues its motion through the system, the leadingedge triggers the outlet unit 513 to close the switch thereof. As thelength of the bank note is greater than the distance along the bank notepath between the units 509 and 513 the means controlling acceptance orrejection of the bank note is released to return to its initialrejection position. When the trailing edge of the bank note has passedthe unit 509 the supply of current to the line 517 is discontinued andthe system is de-energised.

The pairs of threshold circuits for each photosensitive element arebinary devices. Taking for example the circuits 109 and 110, the circuit109 which determines the upper limit provides a binary output of l untilthe input signal exceeds the preset threshold level whereupon the outputwill change into a binary In the case of the circuit 110 whichdetermines the lower level, the output will be a binary 0 until theinput signal reaches the lower threshold limit when it would change to abinary 1.

Thus the outputs of the two threshold circuits will vary as follows forthe various input conditions:

0 and I when the input signal is lower than threshold level of bothcircuits;

l and l when the input signal exceeds the threshold of the lower limitthreshold circuit but does not exceed the threshold of the upper limitthreshold circuit; and

l and 0 when the input signal is greater than that of the thresholdlevels of both circuits.

Once the input signal to a threshold circuit has exceeded the thresholdlevel the output will remain at binary l until the circuit is reset, forexample by the de-energisation followed by re-energisation of thecircuit. The outputs of the different threshold circuits are applied totheir respective AND gates 114, 216, 120, 126 and 222 which will only betriggered if all the signals applied thereto are binary l s. It will beappreciated that since the outputs of the threshold circuits arememorised, the input signals to the AND gates will be maintained untilthe threshold circuits are reset.

Considering for example the case of the four threshold circuits 1% to112, if all the threshold circuits provide a binary 1 indicating thatthe watermark of the bank note is considered to be genuine, then the ANDgate 114 will be triggered to provide a binary 1 output in turn. Thisbinary l is applied to the final AND gate 501 and to a switch unit 401.The switching unit will thereupon react and through switches 114B and114C connect the photosensitive element 105 R1 to the threshold circuits116 and 118 in readiness to analyse the print at point A on the banknote. Point A, however, cannot be analysed until the analyser hasanalysed the metal wire in the bank note and accepted 6 it as genuine.if the metal wire is considered genuine then a binary l from the ANDgate 216 will operate the switches 216B and 216C2. When these latterswitches are operated, the output of the photosensitive element 203 D2is connected to the threshold circuits 218 and 220.

Where, during an analysis of point A of the bank note, the signalsderived from the element R1 cause both threshold circuits 116 and 118 toprovide a binary 1 both outputs of the circuits 116 and 118 are fed tothe AND gate 120 which itself then provides a binary l that is fed tothe final AND gate 501. The binary l is simultaneously applied to theswitching unit 401 causing the switch 120C to connect the elements 105R1 to the line 409 and causing the element 105 to be connected to thethreshold circuits 122 and 124 for analysing the point B. on the banknotes.

if the outputs of the threshold circuits 112 and 124 are binary l s thenthe AND gate 126 will also generate a binary l With all the AND gates114, 120, 126, 222 now providing a binary 1 the final AND gate 501 nowalso generates a binary l which will trigger the consent circuit 503 toconnect the acceptance unit 511 with the power supply 505 thusinitiating the collection of the accepted bank note in the correspondingcontainer and the execution of the dispensing of merchandisc.

As soon as the rear edge of the b ank note has left the reset unit 509,the power supply is disconnected from all the analysers and thethreshold circuits, which consequently return to their initialconditions upon reenergisation. The system is thus ready to take anotherbank note.

It will be appreciated that even if only one of the selected features ofthe scanned bank note is not acknowledged as genuine then the final ANDgate will not energise the consent circuit so that the bank note isreturned to the operator and no further operation is authorised.

It will be appreciated that the analysers described need not be limitedto analysing moving bank notes, they can be used to check bank noteslocated in a fixed frame.

Many modifications may be made to the invention as will be apparant tothose skilled in the art and it is intended to encompass any suchmodifications as fall within the spirit and scope of the invention.

We claim:

1. In a document recognition device, an optical analyser comprisingsupport means for supporting a document to be analysed,

light source means mounted to direct light at a predetermined area ofthe document a first photosensitive member mounted to receive from thelight source means, light which has passed through the predeterminedarea of the document and providing an output indicative of the lightreceived,

a second photosensitive member mounted to receive light from the lightsource means that has been reflected from the predetermined area andproviding an output indicative of the light received reference means forestablishing reference ranges for the transparency and reflectivity ofvalid documents, and comparison means connected to receive the outputsignals from the first and second photosensitive members and connectedto the reference means to compare the output signals with the referenceranges to determine validity of the document in dependence upon theresult of the comparison.

2. A device according to claim 1, in which the light source meanscomprises a single light source.

3. A device according to claim 1, in which the light source and thefirst photosensitive member lie along a common axis which extendsthrough and is inclined to the plane of the document, and in which thesecond photosensitive member lies on the same side of the document asthe light source and extends along an axis that intersects the saidcommon axis in the plane of the document and makes the same angle withthe said plane as the said common axis.

4. A device according to claim 1, including another optical analysersimilar to the first mentioned analyser, the light source means of thetwo analysers being located on opposite sides of the document anddirected at the same predetermined area.

5. A device according to claim 1 wherein the two optical analysers arespaced apart in the direction of the plane of the document forsequementially analysing the said predetermined area.

I 6. A bank note recognition system, comprising an inlet analysing meansincluding at least one optical analyser according to claim 1 a bank notediverter first guide means defining a first path for the bank note fromthe inlet through the analysing means to the diverter an outlet secondguide means defining a second path for the bank note from the diverterto the outlet at bank note reception device, third guide means defininga third path from the diverter to the bank note reception device, and

means connecting the output of the optical analyser to control thediverter and cause the diverter to guide the bank note from the first tothe second path if the bank note is considered to be a forgery and toguide the bank note from the first to the third path if the bank note isconsidered to be genu- 7. A system according to claim 6, wherein thefirst path upstream of the analysing means follows a bend.

8. A device according to claim 6 including sensing means located in thefirst guide path upstream of the analyser and responsive to the passageof a bank note there past to activate the analysing means for analysisof the bank note.

9. A device according to claim 6, wherein said first guide meansincludes a first pair of co-operating rollers located at the inlet meanscoupled to the rollers to drive the rollers in one sense in which a banknote fed through the inlet is driven by the rollers along the first pathtowards the analyser feeler means for senzing the thickness of the banknote as it emerges from the rollers and operative when the thicknessexceeds a predetermined limit to cause the means driving the rollers toreverse the sense of rotation of the rollers and return the bank note tothe inlet.

10. A device according to claim 6, wherein said diverter comprises anelectromagnetically operated guide member.

11. A device according to claim 6, wherein the analyser means includesan optical analyser support member, and

means for moving the optical analyser relative to the support memberwhereby to change the predetermined area of the bank note that is to beanalysed.

12. A device according to claim 7, including further sensing meanslocated in the first guide path down stream of the analyser andresponsive to the passage of the trailing edge of the bank note therepast to deactivate the analysing means in readiness for the analysis ofa subsequent bank note.

13. A device according to claim 6 including first sensing means secondsensing means means locating the first and second sensing means in thefirst path and spaced along the first path by a distance just less thanthe length of a bank note, and

means responsive only to the first and second sensing meanssimultaneously sensing the presence of the bank note to allow the banknote to proceed along the first path.

1. In a document recognition device, an optical analyser comprisingsupport means for supporting a document to be analysed, light sourcemeans mounted to direct light at a predetermined area of the document afirst photosensitive member mounted to receive from the light sourcemeans, light which has passed through the predetermined area of thedocument and providing an output indicative of the light received, asecond photosensitive member mounted to receive light from the lightsource means that has been reflected from the predetermined area andproviding an output indicative of the light received reference means forestablishing reference ranges for the transparency and reflectivity ofvalid documents, and comparison means connected to receive the outputsignals from the first and second photosensitive members and connectedto the reference means to compare the output signals with the referenceranges to determine validity of the document in dependence upon theresult of the comparison.
 2. A device according to claim 1, in which thelight source means comprises a single light source.
 3. A deviceaccording to claim 1, in which the light source and the firstphotosensitive member lie along a common axis which extends through andis inclined to the plane of the document, and in which the secondphotosensitive member lies on the same side of the document as the lightsource and extends along an axis that intersects the said common axis inthe plane of the document and makes the same angle with the said planeas the said common axis.
 4. A device according to claim 1, includinganother optical analyser similar to the first mentioned analyser, thelight source means of the two analysers being located on opposite sidesof the document and directed at the same predetermined area.
 5. A deviceaccording to claim 1 wherein the two optical analysers are spAced apartin the direction of the plane of the document for sequementiallyanalysing the said predetermined area.
 6. A bank note recognitionsystem, comprising an inlet analysing means including at least oneoptical analyser according to claim 1 a bank note diverter first guidemeans defining a first path for the bank note from the inlet through theanalysing means to the diverter an outlet second guide means defining asecond path for the bank note from the diverter to the outlet a banknote reception device, third guide means defining a third path from thediverter to the bank note reception device, and means connecting theoutput of the optical analyser to control the diverter and cause thediverter to guide the bank note from the first to the second path if thebank note is considered to be a forgery and to guide the bank note fromthe first to the third path if the bank note is considered to begenuine.
 7. A system according to claim 6, wherein the first pathupstream of the analysing means follows a bend.
 8. A device according toclaim 6 including sensing means located in the first guide path upstreamof the analyser and responsive to the passage of a bank note there pastto activate the analysing means for analysis of the bank note.
 9. Adevice according to claim 6, wherein said first guide means includes afirst pair of co-operating rollers located at the inlet means coupled tothe rollers to drive the rollers in one sense in which a bank note fedthrough the inlet is driven by the rollers along the first path towardsthe analyser feeler means for senzing the thickness of the bank note asit emerges from the rollers and operative when the thickness exceeds apredetermined limit to cause the means driving the rollers to reversethe sense of rotation of the rollers and return the bank note to theinlet.
 10. A device according to claim 6, wherein said divertercomprises an electromagnetically operated guide member.
 11. wherein theanalyser means includes an optical analyser support member, and meansfor moving the optical analyser relative to the support member wherebyto change the predetermined area of the bank note that is to beanalysed.
 12. A device according to claim 7, including further sensingmeans located in the first guide path down stream of the analyser andresponsive to the passage of the trailing edge of the bank note therepast to deactivate the analysing means in readiness for the analysis ofa subsequent bank note.
 13. A device according to claim 6 includingfirst sensing means second sensing means means locating the first andsecond sensing means in the first path and spaced along the first pathby a distance just less than the length of a bank note, and meansresponsive only to the first and second sensing means simultaneouslysensing the presence of the bank note to allow the bank note to proceedalong the first path.